Question

请将问题读到最后，因为它似乎是许多类似其他人的副本，但事实并非如此。大多数其他问题使用带有let关键字的闭包来捕获对象init之前的弱或无主的自我。我没有。

我的代码：

class Singleton : ObserverProtocol {

    static let shared = Singleton()

    private let obs : Observer = Observer.init()

    private init() { self.obs.responder = self }

    func observe(_ object : Any) {}

    fileprivate class Observer : NSObject {
        unowned var responder : ObserverProtocol!
        func observe(_ obj : Any) {
            self.responder.observe(obj)
        }
    }
}

fileprivate protocol ObserverProtocol : class {
    func observe(_ object : Any)
}

当我尝试编译时，我在unowned var responder : ObserverProtocol!

上突出显示错误

'unowned'可能只适用于类和类绑定协议类型，而不是'ObserverProtocol！'

如果我将unowned更改为weak，我可以编译。

显然有一些关于unowned的概念，我不明白，所以如果有人能向我解释，我会很感激。

P.S。我知道类似的多个问题：

UIView, CMDeviceMotionHandler : unowned may only be applied to class and class-bound protocol types

但我想这不是我的情况。

Answer 1

As you already know, unowned cannot be optional but weak may be nil at some point.

From what I understand, unowned variable is different from implicitly unwrapping optionals. Implicit unwrapping is for variables, which may be nil, but we already know this variable is not nil at the exact point of access. However, unowned variable can never be nil at any point.

Thus, you can't use unowned constant of type ObserverProtocol!. You need to get rid of !.

But if you do get rid of !, Observer needs an initializer that initializes responder.

迅速。 unowned只能应用于类和类绑定协议类型。弱者工作得很好

1 个答案: